Hypochlorous acid (HOCl), the active component of household bleach, functions as a powerful antimicrobial during the innate immune response. Despite its widespread use, surprisingly little is known about how bacteria sense and respond to bleach. To our knowledge, no HOCl-sensitive transcriptional regulator has been identified in any organism to date. Preliminary results from our lab implicate the conserved NemR protein as an HOCl-specific transcriptional repressor in E. coli. We have evidence that oxidation by HOCl causes the formation of specific intermolecular disulfide bonds in NemR, which modulate transcriptional activity and induce the expression of genes required for bleach tolerance. I will use both in vitro biochemical approaches and in vivo genetic techniques to examine the role that NemR plays in bacterial bleach resistance. I will investigate the mechanism of HOCl sensing by analyzing the role of conserved cysteine residues in NemR and the structural and functional changes in NemR that occur upon HOCl-treatment. The results of this study will have potentially broad implications on our understanding of how cells sense HOCl and repair cellular damage. Excessive HOCl-production is implicated in the progression of many human diseases, including chronic inflammation, atherosclerosis and cancer and in bacterial interactions with the human immune system. PUBLIC HEALTH RELEVANCE: The project proposed in this application will provide insights into how bacteria sense and respond to the oxidative stress effects of hypochlorous acid, the active antimicrobial component of bleach. This work is relevant to human health not only because bleach is a commonly used disinfectant, but also because hypochlorous acid is an important antimicrobial compound produced by the white blood cells of the immune system.